Yes, it is possible to copy items or to move items from one collection to another. There are two ways of assigning, which are explained below.
1. Assigning the clip to a new collection
You can simply drag the clip to another collection. Select the clip in question by clicking the dragging symbol and drag it to the new collection.
You can also assign the clip to another collection. In the screenshot below, you can see a view of our collection 'Animals'. As you can see, the video in the red field doesn't really belong there; it should be moved to our new collection called 'Plants'.
Firstly, click the little three dots. A small menu will appear. Hit 'assign to collection'.
A dialog will appear like the one below. This is where you either choose a new collection, or you can also make a new collection here. In our case, we will select the collection called 'Plants'.
After you hit the 'Save button' and you go to the 'Plants' collection, you will see that the video now appears there.
2. Unlinking from the previous collection
Whether you use the assign option or the drag&drop, the clip will appear now in both collections, 'Animals' and 'Plants'. If you don't want a duplicate, then you need to remove the clip from the first collection by unlinking it. Again, there are two options for how to do this.
Note: if you don't break the link with the previous collection, then you will simply have the clip in both collections.
Go back to the original collection, 'Animals' and select the clip. Once you've selected it, you will see a red icon popping up on top. If you hover over it, it reads 'Remove selected items from Nature shots / Animals'. Click that button to remove the clips from this collection and that's it, you're done.
There is one other way to break the link with the previous collection. If you select the clip and click on the 'Assign' button, you will see a dialogue pop up.
In this dialogue, you can see which collections this clip is assigned to. You can also unlink the clip here, by clicking the green x.